worked on some stuff and finally the new install script (no idea if it works yet)

awesome/src/tools/helpers/backlight.lua

@@ -1,6 +1,7 @@
 local aspawn = require('awful.spawn')
 local gobject = require('gears.object')
 local gtable = require('gears.table')
+local gtimer = require('gears.timer')
 
 local backlight = {}
 
@@ -8,17 +9,25 @@ local instance = nil
 
 function backlight.brightness_get_async(callback)
   aspawn.easy_async_with_shell('brightnessctl get', function(stdout)
-    callback(tonumber(stdout:gsub('\n', '')))
+    callback(stdout:gsub('\n', ''))
   end)
 end
 
 function backlight:brightness_increase()
-  aspawn('brightnessctl set 2+%')
+  if not self.allow_cmd then return end
+  self.allow_cmd = false
+  aspawn.easy_async_with_shell('brightnessctl set 2+%', function()
+    self.allow_cmd = true
+  end)
   self:emit_signal('brightness_changed')
 end
 
 function backlight:brightness_decrease()
-  aspawn('brightnessctl set 2-%')
+  if not self.allow_cmd then return end
+  self.allow_cmd = false
+  aspawn.easy_async_with_shell('brightnessctl set 2-%', function()
+    self.allow_cmd = true
+  end)
   self:emit_signal('brightness_changed')
 end
 
@@ -32,6 +41,11 @@ local function new()
     self.max_brightness = tonumber(stdout:gsub('\n', '') or 1)
   end)
 
+  --  Function locker to avoid spawning more commands than can be processed at a time
+  self.allow_cmd = true
+
+  self:emit_signal('brightness_changed')
+
   return self
 end